Syria conflict: Aleppo bombed by fighter planes
Fighter jets have bombed eastern areas of Syria's second city Aleppo, a BBC reporter near the city says.
The attack, which followed an artillery barrage, is seen as a significant escalation in the conflict.
Rebels launched an offensive against Aleppo at the weekend in an attempt to wrest the city from government forces.
US Secretary of State Hillary Clinton says territorial gains made by the rebels will eventually result in a "safe haven" inside Syria.
"We have to work closely with the opposition, because more and more territory is being taken," she told reporters in Washington. That would become a safe haven which would provide a base for further action by the opposition, she said.
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At the scene
BBC News, near Aleppo
The military's response today marked a sharp escalation in this battle.
Helicopter gunships spun through the skies throughout the day. Sustained artillery and mortar rounds pounded restive neighbourhoods.
But it was what happened late in the afternoon that underlined the grave risk to the government of losing ground in what is Syria's largest city and its economic capital.
First came an unmistakeable sound that has so far been absent in this conflict - the roar of fighter jets. What appeared to be Russian-made MiG planes arced through the sky.
We watched as they dropped in, bombing and strafing rebel positions.
Dead and wounded civilians and fighters were taken to hospitals and makeshift clinics as the human cost of this conflict continues to grow.
- Warplanes hit Aleppo
Mrs Clinton said the pace of events was accelerating inside Syria and called on the opposition to be prepared for a transition of power, adding that it was not yet too late for President Assad himself to prepare for such a handover.
In one of the deadliest incidents of the day, opposition activists reported that at least 20 worshippers were killed as they went into a mosque in a village close to the city of Hama.
Troops and militia loyal to President Assad left a roadblock and opened fire on the men who were arriving for evening prayers in Shariaa, one activist told Reuters news agency.
Foreign journalists work under intense restrictions in Syria so reports by both sides are hard to verify.
Earlier in Aleppo, government forces launched what correspondents described as a co-ordinated attack on the Tariq al-Bab area in the east of the city late on Tuesday afternoon, first with a 10-minute barrage of 30 shells and then with bombing runs from fixed-wing jets.
It was thought to be the first time that Syrian fighter planes had been used for bombing urban targets during the conflict, as the government attempted to take back districts of Syria's commercial centre seized by the rebels.
There are reports of dozens of casualties and widespread damage. The BBC's Ian Pannell, on the outskirts of Aleppo, says civilians and fighters are among the dead and wounded.
Helicopter gunships have been involved in the clashes in the city throughout the day, he says.
Fierce fighting has been reported close to the historic Old City. A French correspondent there has spoken of rebels besieging a police headquarters close to the walls of the Old City, which is a world heritage site.